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991.
Nicolini C Kraineva J Khurana M Periasamy N Funari SS Winter R 《Biochimica et biophysica acta》2006,1758(2):248-258
We report on the effects of temperature and pressure on the structure, conformation and phase behavior of aqueous dispersions of the model lipid "raft" mixture palmitoyloleoylphosphatidylcholine (POPC)/bovine brain sphingomyelin (SM)/cholesterol (Chol) (1:1:1). We investigated interchain interactions, hydrogen bonding, conformational and structural properties as well as phase transformations of this system using Fourier transform-infrared (FT-IR) spectroscopy, small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC) coupled with pressure perturbation calorimetry (PPC), and Laurdan fluorescence spectroscopy. The IR spectral parameters in combination with the scattering patterns from the SAXS measurements were used to detect structural and conformational transformations upon changes of pressure up to 7-9 kbar and temperature in the range from 1 to about 80 degrees C. The generalized polarization function (GP) values, obtained from the Laurdan fluorescence spectroscopy studies also reveal temperature and pressure dependent phase changes. DSC and PPC were used to detect thermodynamic properties accompanying the temperature-dependent phase changes. In combination with literature fluorescence spectroscopy and microscopy data, a tentative p,T stability diagram of the mixture has been established. The data reveal a broad liquid-order/solid-ordered (lo+so) two-phase coexistence region below 8+/-2 degrees C at ambient pressure. With increasing temperature, a lo+ld+so three-phase region is formed, which extends up to approximately 27 degrees C, where a liquid-ordered/liquid-disordered (lo+ld) immiscibility region is formed. Finally, above 48+/-2 degrees C, the POPC/SM/Chol (1:1:1) mixture becomes completely fluid-like (liquid-disordered, ld). With increasing pressure, all phase transition lines shift to higher temperatures. Notably, the lo+ld (+so) phase coexistence region, mimicking raft-like lateral phase separation in natural membranes, extends over a rather wide temperature range of about 40 degrees C, and a pressure range, which extends up to about 2 kbar for T=37 degrees C. Interestingly, in this pressure range, ceasing of membrane protein function in natural membrane environments has been observed for a variety of systems. 相似文献
992.
993.
ABCA1 mediates high-affinity uptake of 25-hydroxycholesterol by membrane vesicles and rapid efflux of oxysterol by intact cells 总被引:1,自引:0,他引:1
Tam SP Mok L Chimini G Vasa M Deeley RG 《American journal of physiology. Cell physiology》2006,291(3):C490-C502
ATP Binding Cassette (ABC) transporter, ABCA1, plays a pivotal role in reverse cholesterol transport by mediating the cellular efflux of phospholipid and cholesterol. Studies using intact cells strongly suggest that ABCA1 acts as a phospholipid floppase, but there has been no direct demonstration that the protein is a primary active sterol transporter. Using membrane vesicles from insect Sf21 cells, we found that ABCA1 mediated ATP-dependent uptake of [3H]25-hydroxycholesterol with an apparent Km of 0.7 µM. Consistent with this high apparent affinity, expression of ABCA1 in human embryonic kidney cells both increased rapid efflux of 25-hydroxcholesterol and prevented oxysterol-mediated repression of low-density lipoprotein (LDL) receptor and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase mRNAs. Comparison of wild-type and ABCA1/ murine fibroblasts indicates that 25-hydroxycholesterol is effluxed 5-fold more rapidly by wild-type cells. In addition, the rate of efflux from the wild-type but not the ABCA1/ fibroblasts is increased a further twofold by inducers of ABCA1 expression. Thus under the experimental conditions employed, endogenous ABCA1 is a major contributor to 25-hydroxycholesterol efflux from wild-type fibroblasts. Evidence from in vitro studies indicates that oxysterols are potent inducers of genes involved in cellular cholesterol efflux and metabolism, including the ABCA1 gene, and repressors of genes involved in cholesterol synthesis or uptake. Our observations raise the possibility that efflux of oxysterols by ABCA1 could contribute to a homeostatic mechanism, which both attenuates oxysterol-induced expression of its cognate gene and alleviates repression of genes encoding proteins, such as HMG-CoA reductase and LDL receptor. active transport; cholesterol homeostasis 相似文献
994.
VASP-dependent regulation of actin cytoskeleton rigidity, cell adhesion, and detachment 总被引:2,自引:2,他引:0
Galler AB García Arguinzonis MI Baumgartner W Kuhn M Smolenski A Simm A Reinhard M 《Histochemistry and cell biology》2006,125(5):457-474
Enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) proteins are established regulators of actin-based motility, platelet aggregation, and growth cone guidance. However, the molecular mechanisms involved essentially remain elusive. Here we report on a novel mechanism of VASP action, namely the regulation of tensile strength, contractility, and rigidity of the actin cytoskeleton. Compared to wild-type cells fibroblasts derived from VASP-deficient mice have thicker and more stable actin stress fibres. Furthermore focal adhesions are enlarged, myosin light chain phosphorylation is increased, and the rigidity of the filament-supported plasma membrane is elevated about three- to fourfold, as is evident from atomic force microscopy. Moreover, fibronectin-coated beads adhere stronger to the surface of VASP-deficient cells. The resistance of these beads to mechanical displacement by laser tweezers is dramatically increased in an F-actin-dependent mode. Cytoskeletal stabilization coincides with slower cell adhesion and detachment, while overall adhesion is increased. Interestingly, many of these effects observed in VASP (−/−) cells are recapitulated in VASP-overexpressing cells, hinting towards a balanced stoichiometry necessary for appropriate VASP function. Taken together, our results suggest that VASP regulates surface protrusion formation and cell adhesion through modulation of the mechanical properties of the actin cytoskeleton.Annette B. Galler, Maísa I. García Arguinzonis these authors contributed equally to this work 相似文献
995.
Competition between microorganisms and arthropods has been shown to be an important ecological interaction determining animal
development and spatial distribution patterns in saprophagous communities. In fruit-inhabiting Drosophila, variation in insect developmental success is not only determined by species-specific effects of various noxious filamentous
fungi but, as suggested by an earlier study, also by additive genetic variation in the ability to successfully withstand the
negative impact of the fungi. If this variation represents a direct adaptive response to the degree to which insect breeding
substrates are infested with harmful fungi, genetic variation for successful development in the presence of fungi could be
maintained by variation in infestation of resource patches with fungi. We selected for the ability to resist the negative
influence of mould by maintaining replicated Drosophila melanogaster populations on substrates infested with Aspergillus nidulans. After five cycles of exposure to the fungus during the larval stage, the selected populations were compared with unselected
control populations regarding adult survival and reproduction to reveal an evolved resistance against the fungal competitor.
On fungus-infested larval feeding substrates, emerged adults from mould-selected populations had higher survival rates and
higher early fecundity than the control populations. In the unselected populations, females had higher mortality rates than
males, and a high proportion of both females and males appeared to be unable to lay eggs or fertilise eggs, respectively.
When larvae developed on non-infested food we found indications of a loss of resistance to abiotic and starvation stress in
the adult stage in flies from the selected populations. This suggests that there are costs associated with an increase in
resistance against the microbial competitor. We discuss the underlying mechanisms that might have selected for increased resistance
against harmful fungi. 相似文献
996.
Seven cyanopyridone derivatives and one corresponding seco compound have been isolated from a methanolic extract of the inflorescences and leaves of Acalypha indica L. (Euphorbiaceae). The absolute configuration of the main cyanogenic glucoside acalyphin, (−)-(5R,6S)-5-cyano-5-β-d-glucopyranosyloxy-6-hydroxy-4-methoxy-1-methyl-2(5,6-dihydro)-pyridone, was deduced from an X-ray crystallographic study. In addition, the 6R-epimer of acalyphin, epiacalyphin, and the corresponding pair of N-demethyl derivatives were isolated. The corresponding amide of acalyphin and a 1′,2′-glucosyl-fused epiacalyphin amide were isolated from air-dried material. Structural elucidation was performed by means of 1H and 13C NMR-spectra, chiroptical methods such as CD-spectroscopy and optical rotation. Two further corresponding derivatives, an aromatized compound and an open-chain structure, were isolated from the aqueous phase. 相似文献
997.
Agnieszka Bajda Dorota Konopka-Postupolska Magdalena Krzymowska Jacek Hennig Karolina Skorupinska-Tudek Liliana Surmacz Jacek Wójcik Zdzislaw Matysiak Tadeusz Chojnacki Ewa Skorzynska-Polit Maria Drazkiewicz Pawel Patrzylas Monika Tomaszewska Magdalena Kania Malgorzata Swist Witold Danikiewicz Wieslawa Piotrowska and Ewa Swiezewska 《Physiologia plantarum》2009,135(4):351-364
Infection with avirulent pathogens, tobacco mosaic virus (TMV) or Pseudomonas syringae pv. tabaci induced accumulation of polyisoprenoid alcohols, solanesol and a family of polyprenols [from polyprenol composed of 14 isoprene units (Pren-14) to -18, with Pren-16 dominating] in the leaves of resistant tobacco plants Nicotiana tabacum cv. Samsun NN. Upon TMV infection, solanesol content was increased seven- and eight-fold in the inoculated and upper leaves, respectively, while polyprenol content was increased 2.5- and 2-fold in the inoculated and upper leaves, respectively, on the seventh day post-infection. Accumulation of polyisoprenoid alcohols was also stimulated by exogenously applied hydrogen peroxide but not by exogenous salicylic acid (SA). On the contrary, neither inoculation of the leaves of susceptible tobacco plants nor wounding of tobacco leaves caused an increase in polyisoprenoid content. Taken together, these results indicate that polyisoprenoid alcohols might be involved in plant resistance against pathogens. A putative role of accumulated polyisoprenoids in plant response to pathogen attack is discussed. Similarly, the content of plastoquinone (PQ) was increased two-fold in TMV-inoculated and upper leaves of resistant plants. Accumulation of PQ was also stimulated by hydrogen peroxide, bacteria ( P. syringae ) and SA. The role of PQ in antioxidant defense in cellular membranous compartments is discussed in the context of the enzymatic antioxidant machinery activated in tobacco leaves subjected to viral infection. Elevated activity of several antioxidant enzymes (ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and superoxide dismutase, especially the CuZn superoxide dismutase isoform) and high, but transient elevation of catalase was found in inoculated leaves of resistant tobacco plants but not in susceptible plants. 相似文献
998.
Possible participation of mitochondria in lipid yolk formation in oocytes of paddlefish and sturgeon 总被引:1,自引:0,他引:1
The ovary of paddlefish and sturgeons (Acipenseriformes) is composed of discrete units: the ovarian nests and ovarian follicles.
The ovarian nests comprise oogonia and numerous early dictyotene oocytes surrounded by somatic prefollicular cells. Each ovarian
follicle consists of a spherical oocyte and a layer of follicular cells situated on a thick basal lamina, encompassed by thecal
cells. The cytoplasm of previtellogenic oocytes is differentiated into two distinct zones: the homogeneous and granular zones.
The homogeneous cytoplasm is organelle-free, whereas the granular cytoplasm contains numerous organelles, including mitochondria
and lipid droplets. We have analyzed the cytoplasm of early dictyotene and previtellogenic oocytes ultrastructurally and histologically.
In the cytoplasm of early dictyotene oocytes, two morphologically different types of mitochondria can be distinguished: (1)
with well-developed cristae and (2) with distorted and fused cristae. In previtellogenic oocytes, the mitochondria of the
second type show various stages of cristae distortion; they contain and release material morphologically similar to that of
lipid droplets and eventually degenerate. This process of mitochondrial transformation is accompanied by an accumulation of
lipid droplets that form a single large accumulation (lipid body) located in the vicinity of the oocyte nucleus (germinal
vesicle). The lipid body eventually disperses in the oocyte center. The possible participation of these mitochondria in the
formation of oocyte lipid droplets is discussed.
This work was supported by funds from the research grant BW/IZ/2005 to M.Ż.
An erratum to this article can be found at http://dx.doi.org/.
An erratum to this article can be found at 相似文献
999.
Aneta Monika Białkowska Hubert Cieśliński Karolina Maria Nowakowska Józef Kur Marianna Turkiewicz 《Archives of microbiology》2009,191(11):825-835
A psychrotrophic bacterium producing a cold-adapted β-galactosidase upon growth at low temperatures was classified as Arthrobacter sp. 20B. A genomic DNA library of strain 20B introduced into Escherichia coli TOP10F′ and screening on X-Gal (5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside)-containing agar plates led to the isolation of β-galactosidase gene. The β-galactosidase gene (bgaS) encoding a protein of 1,053 amino acids, with a calculated molecular mass of 113,695 kDa. Analysis of the amino acid sequence
of BgaS protein, deduced from the bgaS ORF, suggested that it is a member of the glycosyl hydrolase family 2. A native cold-adapted β-galactosidase was purified
to homogeneity and characterized. It is a homotetrameric enzyme, each subunit being approximately 116 kDa polypeptide as deduced
from native and SDS–PAGE, respectively. The β-galactosidase was optimally active at pH 6.0–8.0 and 25°C. P-nitrophenyl-β-d-galactopyranoside (PNPG) is its preferred substrate (three times higher activity than for ONPG—o-nitrophenyl-β-d-galactopyranoside). The Arthrobacter sp. 20B β-galactosidase is activated by thiol compounds (53% rise in activity in the presence of 10 mM 2-mercaptoethanol),
some metal ions (activity increased by 50% for Na+, K+ and by 11% for Mn2+) and inactivated by pCMB (4-chloro-mercuribenzoic acid) and heavy metal ions (Pb2+, Zn2+, Cu2+). 相似文献
1000.
Ulrike Kloiber Bettina Pflugfelder Christian Rinke Monika Bright 《Symbiosis (Philadelphia, Pa.)》2009,47(1):43-50
Chemolithoautotrophic, sulphide-oxidizing (thiotrophic) symbioses represent spectacular adaptations to fluctuating environmental
gradients and survival is often accomplished when growth is fuelled by sufficient nourishment through the symbionts leading
to fast cell proliferation. Here we show 5′-bromo-2′ deoxyuridine (BrdU) pulse labelling of vegetative growingZoothamnium niveum, a colonial ciliate obligately associated with thiotrophic ectosymbionts, and demonstrate age related growth profiles in
three heteromorphic host cell types. At the colony’s apex, a large top terminal zooid performed high proliferation activity,
which decreased significantly with increasing colony age but was still present in old colonies indicating that this cell possesses
lifelong cell division potential. In contrast, terminal branch zooids proliferated independent of colony age but appeared
to be limited by their cell division capacity predetermined by branch size, thus leading to the strict, feather-shaped colony
form. Appearance of labelled terminal branch zooids allowed us to distinguish a highly proliferating apical colony region
from an almost inactive, senescent basal region. In macrozooids attached to the colony, extensive BrdU labelling suggests
that DNA synthesis occurs in preparation for a new generation. As motile swarmers, the macrozooids seem to be arrested in
the cell cycle and mitosis and cell division occur when the swarmer settles and transforms into a top terminal zooid buildingup
a new colony. 相似文献